System and method for identifying multiple paths between network nodes

ABSTRACT

Aspects of the invention pertain to transmitting packet data across a computer network. The packets may be sent via one or more distinct routes from a source to a destination. Each route may employ multiple routers disposed along the network. Non-colliding routes are determined by transmitting pairs of probe packets along the routes. A first probe packet has a maximal length, and a second probe packet has a minimal length. Depending on the order of arrival of the probe packets, the system determines whether two transport layer ports at the destination device collide. If there is a collision, then the system searches for a set of non-colliding ports. Once the non-colliding ports are determined, application data may be sent as packets along the different routes to those ports.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to routing data in computer networks. More particularly, the invention pertains to identifying multiple paths between source and destination nodes in computer networks.

2. Description of Related Art

With a networked computer, it is possible to increase the communication bandwidth or the availability of network connectivity by using multiple interfaces concurrently to aggregate bandwidth. One strategy of bandwidth aggregation is known as Link Aggregation (“LAG”). Another is known as Equal Cost Multiple Path (“ECMP”).

Such strategies allow router or switch nodes in the network to load balance traffic across multiple outgoing links. The outgoing link of a packet is often determined based on the hash value of information (source IP address, destination IP address, source port, destination port) in the packet header. A node may maximize its application throughput to a destination by identifying a set of port pairs (source port, destination port) to send traffic across multiple paths available to the destination.

However, specific implementations of such bandwidth allocation, e.g., the use of hashing functions on switches/routers, are often proprietary. Furthermore, the results of such hashing functions may depend on the seed value of individual switches. It is not feasible for a source node to determine a priori if port pairs are to be hashed to different paths to a destination node, especially in wide area network where end hosts have little knowledge of network topologies and router/switch configurations in between them.

In contrast, the invention provides non-proprietary systems and methods that identify and employ multiple paths between network nodes.

SUMMARY OF THE INVENTION

In one embodiment, a method for identifying ports to support data packet traffic between a source device and a destination device in a computer network is provided. The method comprises setting a set S_(D) of destination ports p the destination device is configured to listen to; selecting a subset S_(k) ^(D) from the set S_(D) for serving the data packet traffic between the source device and the destination device; choosing a port p in the set S_(D) for analysis; determining whether the chosen port p collides with any of the ports in the subset S_(k) ^(D); and if there is a collision involving the chosen port p, eliminating the chosen port p from the set S_(D).

In one example, the chosen port p is removed from the set S_(D) prior to determining whether there is a collision. In another example, if there is no collision, the method further comprises modifying the subset S_(K) ^(D) according to the following equation: S_(K) ^(D) _(modified)=S_(K) ^(D) U {p}. In this case, the method may further comprise repeating the selecting, choosing, determining and eliminating operations for k rounds, wherein a new port p is chosen in each round. In one alternative, after each port p is identified that does not collide with any of the ports in the subset S_(D) ^(K), the method further comprises sending the data packet traffic from the source device to the destination device via at least two of the non-colliding ports.

In another example, determining whether the chosen port p collides with any of the ports in the subset S_(k) ^(D) includes transmitting a pair of probe packets from the source device to the destination device. In one alternative, a first one of the pair of probe packets is of a maximum packet transmission size. In this case, a second one of the pair of probe packets may be of a minimum packet transmission size. And in a further example, the port p is randomly selected from the set S_(D).

In accordance with another embodiment, a method of determining port collisions when transmitting traffic between a source device and a destination device in a computer network is provided. The method comprises setting a set S_(D) of destination ports p the destination device is configured to listen to; selecting a subset S_(k) ^(D) from a set S_(D) for serving the data packet traffic between the source device and the destination device; initializing a test subset of ports S_(Y) to be equal to S_(K) ^(D); choosing a port p′ from the set S_(Y) and choosing a port p from the set S_(D) but not in S_(k) ^(D) for analysis; sending a pair of probe packets from the source device to the destination device via p and p′; evaluating arrivals of the pair of the probe packets at the destination device to determine if there is a collision at ports p and p′; and if there is no collision, then identifying port p as a selected port for transmitting data packets between the source device and the destination device.

In one example, the destination device sends an acknowledgement to the source device upon the arrival of the pair of probe packets. Here, the acknowledgement may identify whether there is a collision between p and p′.

In another example, the port p′ is removed from S_(Y) upon choosing. In this case, the method may further comprise repeating the choosing, sending, evaluating and identifying operations for each port in S_(Y) until all of the ports have been removed from S_(Y).

In yet another example, a first one of the pair of probe packets is of a maximum packet transmission size and a second one of the pair of probe packets is of a minimum packet transmission size. In this case, a collision may be determined if the pair of probe packets are received in order of transmission.

In accordance with another embodiment, a processing system for transmission of data packets between a source device and a destination device in a computer network is provided. Here, the computer network includes a plurality of nodes for routing the data packets between the source and destination devices. The processing system comprises a memory for storing data and a processor operatively coupled to the memory for reading the data from and writing the data to the memory. The processor is configured to select a subset S_(k) ^(D) from a set S_(D) of ports p the destination device is configured to listen to. The subset S_(k) ^(D) is configured to serve the data packet traffic between the source device and the destination device. The processor is further configured to choose a port p in the set S_(D) for analysis, to determine whether the chosen port p collides with any of the ports in the subset S_(k) ^(D), and, if there is a collision involving the chosen port p, to eliminate the chosen port p from the set S_(D).

In one example, the processor determines whether the chosen port p collides with any of the ports in the subset S_(k) ^(D) by transmitting a pair of probe packets to the destination device. In this case, the processor may determine whether there is a collision based upon an order of arrival of the transmitted probe packets. In an alternative, the processor comprises the source device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a computer network for use with aspects of the invention.

FIG. 2 illustrates aspects of a network having multiple routes in accordance with the invention.

FIG. 3 is a flow diagram for identifying suitable paths to a given destination port according to aspects of the invention.

FIG. 4 is a flow diagram for determining collisions among ports of a destination node according to aspects of the invention.

FIG. 5 illustrates cross traffic increasing dispersion in a network.

And FIG. 6 illustrates cross traffic decreasing dispersion in a network.

DETAILED DESCRIPTION

Aspects, features and advantages of the invention will be appreciated when considered with reference to the following description of preferred embodiments and accompanying figures. The same reference numbers in different drawings may identify the same or similar elements. Furthermore, the following description is not limiting; the scope of the invention is defined by the appended claims and equivalents.

FIG. 1 presents a schematic diagram of a computer network 100 depicting various computing devices that can be used in a networked configuration in accordance with aspects of the invention. For example, computer network 100 may have a plurality of computers 102, 104, 106 and 108 as well as other types of devices such as portable electronic devices such as a mobile phone 110 and a PDA 112. Such computing devices may be interconnected via a local or direct connection 114 and/or may be coupled via a communications network 116 such as a LAN, WAN, the Internet, etc. The communications network 116 may include multiple nodes comprising switches or routers, as will be discussed below.

Each computing device may include, for example, one or more processing devices (e.g., a CPU) and have user inputs such as a keyboard 118 and mouse 120 and/or various other types of input devices such as pen-inputs, joysticks, buttons, touch screens, etc., as well as a display 122, which could include, for instance, a CRT, LCD, plasma screen monitor, TV, projector, etc. Each computer 102, 104, 106 and 108 may be a personal computer, server, etc. By way of example only, computers 102 and 106 may be personal computers while computer 104 may be a server and computer 108 may be a laptop.

Each computer such as computers 102 and 104 contains a processor, memory/storage and other components typically present in a computer. For instance, memory/storage stores information accessible by processor, including instructions that may be executed by the processor and data that may be retrieved, manipulated or stored by the processor. The memory/storage may be of any type or any device capable of storing information accessible by the processor, such as a hard-drive, ROM, RAM, CD-ROM, flash memories, write-capable or read-only memories. The processor may comprise any number processing elements, such as sub-processing units operating in a parallel-processing configuration. Alternatively, the processor may be a dedicated controller for executing operations, such as an ASIC.

The communications network 116 is preferably configured to handle data packets (e.g., packets P₁ and P₂) using one or more nodes. FIG. 2 illustrates a network configuration 200, where a source device 202 (e.g., computer 102) may send data to a destination device 204 (e.g., computer 104) via one or more nodes 206 in the network. As shown, each node may comprise a router/switch such as router R₀, R_(I), etc.

The routers may include a processor such as a CPU, as well as memory for storing/queuing buffered data packets. The packets are preferably queued in a first-in, first-out (“FIFO”) order. The routers may be arranged in the network so that packets from the source device 202 may be passed to the destination device 204 via multiple alternative routes. Identifying such routes enables the system to efficiently route the packets. By way of example, FIG. 2 illustrates a first path 208 along the route R₀, R_(L), R_(L+1) ¹, R_(M) ¹ and R_(M+1), as well as a second path 210 along the route R₀, R_(L), R_(L+1) ², R_(M) ² and R_(M+1).

In accordance with aspects of the invention, several propositions or requirements regarding analyzing packet routing through the network are set forth. The first proposition is that there is no out of order delivery of packets sent from the source device to the destination device if these packets traverse the same route, unless a link failure occurs and causes a route change at a router in between its transmissions of these packets.

A second proposition is that if two consecutive packets traverse different routes, they may arrive out of order at the destination. The probability of out of order delivery is maximized when the size of first probe packet is maximized and that of second probe packet is minimized.

And a third proposition is that if two consecutive probe packets P₁ and P₂ of respective lengths L_(max) and L_(min) (e.g., the largest and smallest packet lengths supported by node R₀) traverse different routes yet arrive in order at the destination, the path traversed by P₂ experiences much larger queuing and/or transmission delay than P₁. In this case, it may be of little gain to split the data traffic across the two paths traversed by P₁ and P₂, since the throughput improvement is marginal.

Assume source device 202 is configured to initiate a data intensive application (such as a file transfer) that sends a large amount of traffic (e.g., 10 Mbytes) from its port X to destination device 204. According to one aspect, S_(D) is defined as a set of destination ports p the destination device 204 is listening to and can receive data from the source device 202. In this embodiment, the invention allows the source device 202 or other associated device to discover N paths each served by a destination port in S_(N) ^(D) (S_(N) ^(D)⊂S_(D)) of the destination device 204. The source device 202 thus can split its traffic across these N paths, for example by establishing N TCP/UDP sessions, one to each destination port in S_(N) ^(D).

In one embodiment, a process is executed iteratively to arrive at a solution. FIG. 3 illustrates a flow diagram 300 for identifying multiple paths to a given destination device and a set of ports on the destination serving these paths. The process desirably executes iteratively for up to N−1 rounds. As shown in block 302, a counter k of the rounds is incremented (and which may be initialized to 0). In the k^(th) round, the process starts with S_(k) ^(D), which is a subset of k ports in S_(D) to serve traffic from the source device to the destination device over k unique paths. This is done to discover the (k+1)^(th) path from the source to the destination, as well as a port p in S_(D) to serve packets traversing this path. This process is desirably done by exchanging at least one probe pair or acknowledgement (“ACK”) packet between the source device and the destination device.

In one example, two destination ports, namely p₁, and p₂, “collide” if packets destined to p₁ traverse the same path as those destined to p₂. The source device (e.g., router R₀ or source 202) searches for a port p in S_(D) that does not collide with any ports in S_(k) ^(D), and eliminates ports from S_(D) that collide with ports in S_(k) ^(D). First, in block 304 a port p is removed from S_(D). Preferably, the port p is randomly selected for removal in block 304. Then, in block 306, it is determined if the port p just removed from S_(D) collides with any port in S_(k) ^(D). If so, the removed port p is not added back to S_(D) such that it is skipped in the next round k+1, and the process returns to block 302. If there is no collision, the process proceeds to block 308, where S_(k+1) ^(D) is assigned to be S_(k+1) ^(D)=S_(k) ^(D)∪p. Here, port p is added to S_(k+1) ^(D). The “∪” symbol in this equation is a union or addition operator.

As shown in block 310, if the counter k is less than N−1, then the process returns to block 302; otherwise it ends at block 312.

To determine if a given port p collides with any port in S_(k) ^(D) without modifying S_(k) ^(D), the process 400 shown in FIG. 4 may be employed. First, as shown in block 401, a set of ports S_(Y) is initialized to be the same as the set of ports in S_(K) ^(D). As shown in block 402, a port p′ is removed from the set S_(Y). The port p′ is preferably randomly selected for removal from S_(Y).

Next, as shown in block 404, for each port p′ in S_(k) ^(D), a pair of probe packets is sent back to back via ports p′ and p respectively. The size of the first probe packet is preferably a maximum transmission unit (L_(MAX)) supportable by the network between the source 202 and the destination 204, while the second probe is preferably of a minimum packet length (L_(MIN)) supported by the network between the source 202 and destination 204. The destination device 204 may send an acknowledgement ACK back to the source device 202, as shown in block 406.

As shown in block 408, the ACK may indicate whether the ports p and p′ collide. In particular, if the destination device 204 received the two probe packets out of order, it is determined that ports p′ and p do not collide at block 410. If the packets are received in order, it is determined that p′ and p collide (e.g., port p collides with port p′ in S_(k) ^(D)) as shown in block 412.

As shown in block 414 if S_(Y) is not empty, the process preferably returns to block 402 and repeats until a port p′ is found in S_(Y) that collides with p, or until it is determined that no ports in S_(Y) collides with p. If S_(Y) is empty or a collision is found, the process terminates at bock 416.

One of the propositions discussed above was that if two consecutive packets traverse different routes, they could arrive out of order at the destination. The probability of out of order delivery is maximized when the size of first probe is maximized and that of second probe is minimized.

To prove this observation, consider the following network model depicting two routes between a source node and a destination node. In this example, two probe packets, P₁ of length L₁, and P₂ of length L₂, are sent back to back from the source node to the destination node. The probe packets each traverses one of two routes, which may initially share certain routers, e.g., R₀, R₁, . . . R_(l). In this example, the two routes branch off after R_(l) and re-merge at R_(m). The transmission rate of a router R (R ε {R_(i)|0≦i≦l}∪{R_(i) ¹|l<i≦m}∪{R_(i) ²|l<i≦m}) is r(R), and Q²(R) and Q¹ (R) represent the queuing delays experienced by P₁ and P₂ at R, respectively.

Assume there is no cross traffic and the queuing delay is zero for P₁ and P₂ at R₀ to R_(l). It is straightforward to prove that:

${T_{l}^{2} - T_{l}^{1}} = \frac{L_{2}}{\min\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq L}} \right\}}$

T_(l) ² and T_(l) ² are the arrival times of P₁ and P₂ at R_(l), and min{r(R_(i))|0≦i≦l} is the bandwidth of bottleneck link between R₀ and R_(l). When there is cross traffic, T_(l) ²−T_(l) ¹, the dispersion of P₁ and P₂, can expand or compress. To express this phenomena, we let:

${T_{l}^{2} - T_{l}^{1}} = {\frac{L_{2}}{\min\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}} + \delta_{c}}$

Cross traffic, such as a packet P₃, may be serviced in between P₁ and P₂. As shown in FIG. 5, if this occurs, then the dispersion between P₁ and P₂ increases. The probability of such cross traffic expanding the dispersion of P₁ and P₂ decreases with the length L₂ of packet P₂. Thus, if the length L₂ of packet P₂ is minimized, the probability of cross traffic packet P₃ increasing the dispersion between P₁ and P₂ is minimized.

If cross traffic P₃ is serviced before P₁ as shown in FIG. 6, the dispersion of P₁ and P₂ is decreased. The probability of such cross-traffic P₃ decreasing the dispersion of P₁ and P₂ increases with the length L₁ of packet P₁. Furthermore, it can be proved that:

${T_{l}^{2} - T_{l}^{1}} \geq \frac{L_{2}}{\max\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}}$

Hence:

$\frac{L^{2}}{\max\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}} \leq {T_{l}^{2} - T_{l}^{1}} \leq \frac{L_{2}}{\min\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}}$

Thus T_(l) ²−T_(l) ¹ is minimized if L₂ is minimized and L₁ is maximized. Next, T_(m) ¹ and T_(m) ², the arrival times of P₁ and P₂ at R_(m), respectively, and the condition for T_(m) ¹>T_(m) ², that is P₂ arrives at R_(m) and eventually at the destination node before P₁ are derived. In particular:

$T_{m}^{1} = {T_{l}^{1} + {Q^{1}\left( R_{l} \right)} + \frac{L_{1}}{r\left( R_{l} \right)} + {\sum\limits_{{l + 1} \leq i \leq m}{Q^{1}\left( R_{i}^{1} \right)}} + \frac{L_{1}}{r\left( R_{i}^{1} \right)}}$ $T_{m}^{2} = {T_{l}^{2} + {Q^{2}\left( R_{l} \right)} + \frac{L_{2}}{r\left( R_{l} \right)} + {\sum\limits_{{l + 1} \leq i \leq m}{Q^{2}\left( R_{i}^{2} \right)}} + \frac{L_{2}}{r\left( R_{i}^{2} \right)}}$

T_(m) ²<T_(m) ¹ if and only iff:

${T_{l}^{2} - T_{l}^{1}} < {{Q^{1}\left( R_{l} \right)} - {Q^{2}\left( R_{l} \right)} + \frac{L_{1} - L_{2}}{r\left( R_{l} \right)} + {\sum\limits_{{l + 1} \leq i \leq m}{Q^{1}\left( R_{i}^{1} \right)}} + {\sum\limits_{{l + 1} \leq i \leq m}\frac{L_{1}}{r\left( R_{i}^{1} \right)}} - {\sum\limits_{{l + 1} \leq i \leq m}{Q^{2}\left( R_{i}^{2} \right)}} - {\sum\limits_{{l + 1} \leq i \leq m}\frac{L_{2}}{r\left( R_{i}^{2} \right)}}}$

In the above formula, when L₁ is maximized and L₂ is minimized, T_(l) ²−T_(l) ¹ is minimized, and

$\frac{L_{1} - L_{2}}{r\left( R_{l} \right)} + {\sum\limits_{{l + 1} \leq i \leq m}\frac{L_{1}}{r\left( R_{i}^{1} \right)}} - {\sum\limits_{{l + 1} \leq i \leq m}\frac{L_{2}}{r\left( R_{i}^{2} \right)}}$ is maximized. Assume the sum of queuing delays experienced by P₁ and P₂,

${{Q^{1}\left( R_{l} \right)} + {\sum\limits_{{l + 1} \leq i \leq m}{Q^{1}\left( R_{i}^{1} \right)}}},{{{and}\mspace{14mu}{Q^{2}\left( R_{l} \right)}} + {\sum\limits_{{l + 1} \leq i \leq m}{Q^{2}\left( R_{i}^{2} \right)}}},$ are independent of L₁ and L₂. The probably of T_(m) ²<T_(m) ¹ is maximized when L₁ is maximized and L₂ is minimized.

It can be further proved that if between R_(m) and the destination node, P₁ and P₂ traverse on different routes, the lead time of P₂ over P₁ is also maximized when is L₁ maximized and L₂ is minimized.

With regard to the third proposition, if two consecutive probe packets P₁ and P₂ of length L_(max) and L_(min) (denoting the largest and smallest packet length supported by the network's nodes) traverse different routes yet arrive in order at the destination, the path traversed by P₂ experience much larger queuing and/or transmission delay than P₁. It is thus of little gain to split the application traffic across the two paths traversed by P₁ and P₂, since the throughput improvement is marginal.

When L₁=L_(max) and L₂=L_(min), the probability of cross traffic in between P₁ and P₂ is close to zero, and it may be assumed that:

$\frac{L_{2}}{\max\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}} \leq {T_{l}^{2} - T_{l}^{1}} \leq {{\frac{L_{2}}{\min\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}}T_{l}^{2}} - T_{l}^{1} + {\sum\limits_{l \leq i \leq m}{Q^{2}\left( R_{i}^{2} \right)}} - {\sum\limits_{l \leq i \leq m}{Q^{1}\left( R_{i}^{1} \right)}} + {Q^{2}\left( R_{l} \right)} - {Q^{1}\left( R_{l} \right)} + {\sum\limits_{l \leq i \leq m}\frac{L_{2}}{r\left( R_{i}^{2} \right)}} - {\sum\limits_{l \leq i \leq m}\frac{L_{1}}{r\left( R_{i}^{1} \right)}} + \frac{L_{2} - L_{1}}{r\left( R_{l} \right)}} > 0$ ${\frac{L_{2}}{\min\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}} + {\sum\limits_{l \leq i \leq m}{Q^{2}\left( R_{i}^{2} \right)}} - {\sum\limits_{l \leq i \leq m}{Q^{1}\left( R_{i}^{1} \right)}} + {Q^{2}\left( R_{l} \right)} - {Q^{1}\left( R_{l} \right)} + {\sum\limits_{l \leq i \leq m}\frac{L_{2}}{r\left( R_{i}^{2} \right)}} - {\sum\limits_{l \leq i \leq m}\frac{L_{1}}{r\left( R_{i}^{1} \right)}} + \frac{L_{2} - L_{1}}{r\left( R_{l} \right)}} > 0$

If the queuing delays of P₁ and P₂ are equal,

${\frac{L_{2}}{\min\left\{ {{r\left( R_{i} \right)}❘{0 \leq i \leq l}} \right\}} + {\sum\limits_{l \leq i \leq m}\frac{L_{2}}{r\left( R_{i}^{2} \right)}} + \frac{L_{2}}{r\left( R_{l} \right)} - {\sum\limits_{l \leq i \leq m}\frac{L_{1}}{r\left( R_{i}^{1} \right)}} - \frac{L_{1}}{r\left( R_{l} \right)}} > 0$

Once a pair of non-colliding ports has been found, the system may configure packet transmission to send one or more packets along the different routes from the source node to the destination node. In one alternative, the system evaluates the network to determine whether more than two non-colliding destination ports are present. If so, the packet traffic may be split among all non-colliding routes.

Furthermore, the processes discussed herein, such as the operations discussed with regard to FIGS. 3 and 4, may be performed by one or more processors in the system. By way of example only, processing may be performed by the source device 202, destination device 204 or one of the routers 206 of FIG. 2. The processor(s) may execute a program recorded/stored on a computer-readable recording medium, such as ROM, RAM, flash memory, CD-ROM, DVD-ROM or the like.

Although aspects of the invention herein have been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the invention as defined by the appended claims. 

The invention claimed is:
 1. A method for identifying ports to support data packet traffic between a source device and a destination device in a computer network, the method comprising: setting a set S_(D) of destination ports located at the destination device; identifying a subset of ports S_(k) ^(D) using ports from the set S_(D) by repeating the sub-tasks of: choosing a port p from the set S_(D), the port p not being a member of the subset S_(k) ^(D); determining whether the port p collides with ports from the subset S_(k) ^(D) by transmitting pairs of packets to the destination device, each pair including a first packet transmitted to the port p and a second packet transmitted to one of the ports in the subset S_(k) ^(D), wherein a collision is found to exist when the packets from at least one of the pairs arrive at the destination device in order of transmission, and a collision is found not to exist when the packets from the at least one of the pairs arrive out of order; when it is determined that the port p does not collide with any of the ports in the subset S_(k) ^(D), adding the port p to the subset S_(k) ^(D); and serving data traffic between the source device and the destination device by using the ports from the subset S_(k) ^(D).
 2. The method of claim 1, wherein the chosen port p is removed from the set S_(D) prior to determining whether there is a collision.
 3. The method of claim 1, wherein the port p is randomly selected from the set S_(D).
 4. The method of claim 1, wherein a first one of the pair of probe packets is of a maximum packet transmission size.
 5. The method of claim 4, wherein a second one of the pair of probe packets is of a minimum packet transmission size.
 6. A processing system for transmission of data packets between a source device and a destination device in a computer network, the computer network including a plurality of nodes for routing the data packets between the source and destination devices, the processing system comprising: a memory for storing data; and a processor operatively coupled to the memory for reading the data from and writing the data to the memory, the processor being configured to: select a subset S_(k) ^(D) from a set S_(D) of ports p the destination device is configured to listen to, the ports p in the set S_(D) being located at the destination device, and the ports in the subset S_(k) ^(D) being used in serving the data packet traffic between the source device and the destination device, wherein the processor is further configured to: choose a given one of the ports p in the set S_(D) for analysis, determine whether the given port p collides with any of the ports in the subset S_(k) ^(D) by determining whether a pair of probe packets are received at the destination device in order of transmission, wherein a collision is found to exist when the pair of probe packets arrive in order and a collision is found not to exist when the pair of probe packets arrive out of order, eliminate the chosen port p in response to determining that the given port p collides with any of the ports in the subset S_(k) ^(D), and add the port p to the subset S_(k) ^(D) in response to determining that the given port p does not collide with any of the ports in the subset S_(k) ^(D).
 7. The processing system of claim 6, wherein the processor comprises the source device.
 8. The processing system of claim 6, wherein a first one of the pair of probe packets is of a maximum packet transmission size.
 9. The processing system of claim 8, wherein a second one of the pair of probe packets is of a minimum packet transmission size. 